Walking trajectory control for a biped robot

A not trivial problem in bipedal robot walking is the instability produced by the violent transition between the different dynamic walk phases. In this work an dynamic algorithm to control a biped robot is proposed. The algorithm is based on cubic polynomial interpolation of the initial conditions for the robot’s position, velocity and acceleration. This guarantee a constant velocity an a smooth transition in the control trajectories. The algorithm was successfully probed in the bipedal robot “Dany walker” designed at the Freie Universität Berlin, finally a briefly mechanical description of the robot structure is presented

Ground Reference Points in Legged Locomotion: Definitions, Biological Trajectories and Control Implications

The Zero Moment Point (ZMP) and Centroidal Moment Pivot (CMP) are important ground reference points used for motion identification and control in biomechanics and legged robotics. Using a consistent mathematical notation, we define and compare the ground reference points. We outline the various methodologies that can be employed in their estimation. Subsequently, we analyze the ZMP and CMP trajectories for level-ground, steady-state human walking. We conclude the chapter with a discussion of the significance of the ground reference points to legged robotic control systems. In the Appendix, we prove the equivalence of the ZMP and the center of pressure for horizontal ground surfaces, and their uniqueness for more complex contact topologies. Since spin angular momentum has been shown to remain small throughout the walking cycle, we hypothesize that the CMP will never leave the ground support base throughout the entire gait cycle, closely tracking the ZMP. We test this hypothesis using a morphologically realistic human model and kinetic and kinematic gait data measured from ten human subjects walking at self-selected speeds. We find that the CMP never leaves the ground support base, and the mean separation distance between the CMP and ZMP is small (14 % of foot length), highlighting how closely the human body regulates spin angular momentum in level ground walking

Design and control of a 6 DOF biped robot

This thesis is composed of the following five parts: construction of a 6 Degrees of Freedom (DOF) biped robot, control system design, analysis of forward kinematics and inverse kinematics, walking pattern planning, and PID control implementation. The 6 DOF biped robot is built with aluminum plates, aluminum angles, wood, and rubber materials. It has two legs, two feet, and one trunk, each leg having three joints: hip, knee, and ankle. All joints are actuated by gear head DC motors with built-in encoders. A microcontroller-and-PC-computer-based control system is designed for the biped robot. The control system consists of actuators, sensors, controllers, and a PC computer. The actuators are the gear head DC motors with H-bridge circuits as drivers and the sensors are incremental encoders built in the DC motors. The controllers used are two microcontrollers, one for each leg. The microprocessors read and process joint angle measurements from the encoders and then transmit them to the PC computer. At the same time, the microcontrollers receive control signals from the PC computer and transfer them to the H-bridge circuits to control the robot joints. Data transfer between the microcontrollers and the PC computer is implemented by two RS232 serial communication channels. A control algorithm and walking pattern planning are carried out on the PC computer. Both forward kinematics and inverse kinematics are analyzed based on the D-H representation for the biped robot. Foot trajectories and hip trajectory are calculated by using the 3rd order spline interpolation method. Desired trajectories for joint angles are determined by the inverse kinematics. Simulation is performed to demonstrate the walking pattern. PID controllers are designed for controlling the biped robot to walk according to the designed walking pattern. The proposed PID controllers are implemented on the biped robot

Dynamic balance and walking control of biped mechanisms

The research presented here focuses on the development of a feedback control systems for locomotion of two and three dimensional, dynamically balanced, biped mechanisms. The main areas to be discussed are: development of equations of motion for multibody systems, balancing control, walking cycle generation, and interactive computer graphics. Additional topics include: optimization, interface devices, manual control methods, and ground contact force generation;Planar (2D) and spatial (3D) multibody system models are developed in this thesis to handle all allowable ground support conditions without system reconfiguration. All models consist of lower body segments only; head and arm segments are not included. Model parameters for segment length, mass, and moments of inertia are adjustable. A ground contact foot model simulates compression compliance and allows for non-uniform surfaces. In addition to flat surfaces with variable friction coefficients, the systems can adapt to inclines and steps;Control techniques are developed that range from manual torque input to automatic control for several types of balancing, walking, and transitioning modes. Balancing mode control algorithms can deal with several types of initial conditions which include falling and jumping onto various types of surfaces. Walking control state machines allow selection of steady-state velocity, step size, and/or step frequency;The real-time interactive simulation software developed during this project allows the user to operate the biped systems within a 3D virtual environment. In addition to presenting algorithms for interactive biped locomotion control, insights can also be drawn from this work into the levels of required user effort for tasks involving systems controlled by simultaneous user inputs;Position and ground reaction force data obtained from human walking studies are compared to walking data generated by one of the more complex biped models developed for this project

Otimização de locomoção bípede

Dissertação de mestrado integrado em Engenharia BiomédicaAtualmente verifica-se um crescimento exponencial a nível de desenvolvimento de sistemas robóticos móveis havendo um esforço para criar sistemas com propriedades mais eficientes e adaptáveis às exigências do ambiente de trabalho. Neste contexto, têm havido uma preocupação acrescida em desenvolver melhores sistemas de locomoção quer seja locomoção por rodas quer seja por pernas (bípede, quadrúpede e hexapode). Esta dissertação foca-se na otimização da locomoção bípede a qual é uma área que tem sido alvo de grande atenção uma vez que esta é uma área da robótica que ainda necessita de progredir no sentido de conseguir finalmente uma locomoção tão eficiente como a marcha humana. Deste modo, a elaboração deste trabalho teve como objetivos principais a criação de uma estratégia de otimização que combinasse a geração de padrões de movimento através de geradores centrais de padrões (CPGs) com um algoritmo de otimização evolucionário (Non-Dominated Sorting Genetic Algorithm ll). Essa estratégia implicou a determinação de objetivos que correspondem a características da locomoção bípede e que foram otimizados, sendo eles o deslocamento frontal, a altura a que o pé levanta, a força de impacto entre os pés e o chão e a posição do centro de massa. Os resultados foram obtidos a partir de simulações na plataforma Webots para o robô bípede Darwin-OP. Neste contexto, os resultados foram muito satisfatórios uma vez que o algoritmo foi capaz de gerar locomoção estável e os objetivos propostos foram otimizados. Foi feito também um estudo de sensibilidade que determinou a existência de parâmetros de CPGs que apresentam uma forte correlação positiva com as funções objetivos. Assim, os parâmetros Acompasso, frequência ω e ORoll influenciam fortemente o deslocamento e a força de impacto e o parâmetro AhPitch influencia a altura a que o pé levanta. No futuro seria pertinente aplicar o algoritmo elaborado num robô bípede real e conferir se consegue gerar uma locomoção eficiente em condições reais.Presently there is an exponential increase on the level of development of mobile robotic systems and so there is an effort to create systems with properties more efficient and adaptable to the demands of the work environment. In this context, there has been a heightened concern in developing better systems of locomotion either by wheels either by legs (bipedal, 4-legged or 6-legged). This dissertation focuses on the optimization of bipedal locomotion which is an area that has been the subject of much attention since this is an area of robotics that still needs to make progress towards finally achieving locomotion as efficient as the human gait. Thus, this work aimed to create an optimization strategy that combines the generation of movement patterns through central pattern generators (CPGs) with an evolutionary optimization algorithm (Non-Dominated Sorting Genetic Algorithm II). This strategy involved the determination of objectives that correspond to characteristics of bipedal locomotion and that have been optimized, namely the frontal displacement, the ground clearance, the impact force between the foot and the ground and the position of the center of mass. The results were obtained from simulations in Webots platform for the bipedal robot Darwin-OP. The results were very satisfactory since the algorithm was able to generate stable locomotion and the proposed objectives were optimized. We also made a sensitivity analysis that determined the existence of CPGs parameters that exhibit a strong positive correlation with the objective functions. Thus, the parameters Acompasso, the frequency ω and ORoll strongly influence the impact force and displacement as well as AhPitch influences the height to which the foot rises. In the future it would be appropriate to apply the developed algorithm in a real biped robot and check if it can generate an efficient locomotion in real conditions